PT113 · S2 · Q26 All known deposits of the mineral

Our two premises need to give us this sort of relationship: - this person/thing uses only X. - all known examples of X are from A. We have an only statement: - owls eat only island-frogs So the other premise needs to say - all known examples of island-frogs are from _____ . Instead, we just have a generic idea that "many island-frogs are from the lagoon". Another way of talking about why this answer is bad is that it would be easy to disagree with this conclusion (whereas it wasn't easy to disagree with the original argument's conclusion). There might be tons of frogs on Scrag Island that don't live in the lagoon. In fact maybe 90% of the island's frogs live outside the lagoon, and so the owls will probably eat many frogs that live outside the lagoon.

This conclusion is the wrong strength. We want something that has the strength of probable / likely / unlikely. This conclusion just has possible strength: "they may never eat an animal that lives outside the lagoon." That's the quickest way to avoid having to actually read this / think about it. If we went deeper, we can also see that the two premises do not convince us that owls are only eating lagoon animals. We aren't told anything restrictive about the owls diet. The original conclusion was "Ashley will probably never collect a non-Tanzanian stone" and there was a premise that said "Ashley only collects tanzanite stones". So if we're going to conclude that "an owl will probably never eat any non-lagoon animal", then we should have a premise that says "owls only eat _____ ".

This is fairly close, but the premises don't quite fit as they should. Our two premises need to give us this sort of relationship: - this person/thing uses only X. - all known examples of X are from A. We have an only statement: - owls eat only island-frogs So the other premise needs to say - all known examples of island-frogs are from _____ . Instead, it says "all known lagoon-animals are frogs". We could fight this conclusion as we did with (A). It's very possible that 90% of the frogs on the island live outside the lagoon. Since owls eat only island frogs, it's very possible that they mostly eat stuff that lives outside the lagoon.

This conclusion is the wrong strength. We want something that has the strength of probable / likely / unlikely. This conclusion has certain strength: "no owl will ever eat anything that lives outside the lagoon." We can't actually support a conclusion this strong because we're not 100% sure that owls only eat frogs. We only know them to eat frogs, but it's possible they eat other stuff and we just haven't seen it. Additionally, the two premises in this one mix up which one gets the "all we know of". In the original argument, - Ashley collects only tanzanite stones (definite) - all known deposits of tanzanite are from T In this - owls are known to eat only frogs. - all frogs live in lagoon.